KR20180015718A - The acrylic-based flexible assembly layer - Google Patents

Abstract

The present invention is an assembly layer for a flexible device. The assembly layer is derived from a precursor comprising an alkyl (meth) acrylate ester having from 1 to 24 carbon atoms in the alkyl group, and a free radical-generating initiator. Within a temperature range of from about -30 DEG C to about 90 DEG C, the assembly layer has a shear storage modulus of about 2 MPa or less at a frequency of 1 Hz, an applied shear stress of about 50 kPa to about 500 kPa The shear creep compliance (J) measured at 5 seconds is at least about 6 x 10 < ^-6 > 1 / Pa and within about 1 minute after removal of applied shear stress, The strain recovery at at least one point of the applied shear stress in the flexible device is greater than or equal to about 50%. In a preferred embodiment, the flexible device is a flexible electronic display.

Description

The acrylic-based flexible assembly layer

The present invention generally relates to the field of flexible assembly layers. In particular, the present invention relates to an acrylic-based flexible assembly layer.

Typical applications of pressure sensitive adhesives in the industry today are in the manufacture of a variety of displays such as computer monitors, TVs, cell phones and small displays (in automotive, consumer electronics, wearable, electronic equipment, etc.). Flexible electronic displays, in which the display can flex freely without cracking or breaking, are rapidly emerging technology areas for manufacturing electronic devices, for example, using flexible plastic substrates. These techniques enable the integration of electronic functionality into non-planar objects, the conformity to the desired design, and the flexibility in use that can lead to many new applications.

With the advent of flexible electronic displays, an assembly layer or gap filling between the outer cover lens or sheet (based on glass, PET, PC, PMMA, polyimide, PEN, cyclic olefin copolymers, etc.) and the lower display module of the electronic display assembly There is an increasing need for optically clear adhesives (OCA) for adhesives that act as a gap filling layer. The presence of OCA improves the performance of the display by increasing brightness and contrast, while also providing structural support for the assembly. In the flexible assembly, OCA will also act in the assembly layer, which, in addition to the typical OCA function, can also absorb most of the fold induced stresses to prevent damage to the fragile components of the display panel, The electronic component can be protected from breakage under stress. The OCA layer can be used to position a neutral bending axis at or near at least the brittle component of the display, such as, for example, a barrier layer of an organic light emitting display (OLED), a driving electrode, ≪ / RTI >

When used outside the viewing area of the display or outside the light-active area of the photovoltaic assembly, the flexible assembly layer need not be optically transparent. In practice, such a material may still be useful as a sealant at the periphery of the assembly, for example, to enable movement of the substrate while maintaining sufficient adhesion to seal the device.

A typical OCA is virtually viscoelastic and is intended to provide durability under various environmental exposure conditions and high frequency loading. In such cases, a high level of adhesion and a slight balance of viscoelastic properties are maintained, achieving good pressure-sensitive behavior and incorporating damping properties in the OCA. However, this property is not entirely sufficient to enable foldable or durable displays.

Due to the significantly different mechanical requirements for flexible display assemblies, there is a need to develop novel adhesives for applications in this new technology area. With the usual performance attributes such as optical transparency, adhesion, and durability, such OCA needs to meet a new set of requirements such as bendability and recoverability without defects and delamination.

In one embodiment, the present invention is an assembly layer for a flexible device. The assembly layer comprises an alkyl (meth) acrylate ester having from 1 to 24 carbon atoms in the alkyl group; And a free radical generation initiator. Within a temperature range of from about -30 DEG C to about 90 DEG C, the assembly layer has a shear storage modulus of about 2 MPa or less at a frequency of 1 Hz, an applied shear stress of about 50 kPa to about 500 kPa Of shear creep compliance (J) measured at 5 seconds is greater than or equal to about 6 x 10 < ^-6 > 1 / Pa, and within about 1 minute after removal of applied shear stress, The strain recovery at at least one point of the applied shear stress is at least about 50%.

In another embodiment, the invention is a laminate comprising a first substrate, a second substrate, and an assembly layer positioned between the first substrate and the second substrate and in contact with the first substrate and the second substrate. The assembly layer comprises an alkyl (meth) acrylate ester having from 1 to 24 carbon atoms in the alkyl group; And a free radical generation initiator. Within a temperature range of from about -30 ° C to about 90 ° C, the assembly layer has a shear storage modulus at a frequency of 1 Hz of about 2 MPa or less, measured at 5 seconds with an applied shear stress of about 50 kPa to about 500 kPa Of at least one point of applied shear stress in the range of from about 5 psi to about 500 psi within about one minute after shear stress relief (J) of at least about 6 x 10 < ^-6 > The strain recovery rate is about 50% or more.

In another embodiment, the present invention is a method of bonding a first substrate and a second substrate, wherein both the first substrate and the second substrate are flexible. The method includes positioning an assembly layer between a first substrate and a second substrate, and applying pressure and / or heat to form the laminate. The assembly layer comprises an alkyl (meth) acrylate ester having from 1 to 24 carbon atoms in the alkyl group; And a free radical generation initiator. Within a temperature range of from about -30 ° C to about 90 ° C, the assembly layer has a shear storage modulus at a frequency of 1 Hz of about 2 MPa or less, measured at 5 seconds with an applied shear stress of about 50 kPa to about 500 kPa Of at least one point of applied shear stress in the range of from about 5 psi to about 500 psi within about one minute after shear stress relief (J) of at least about 6 x 10 < ^-6 > The strain recovery rate is about 50% or more.

The present invention is an acrylic-based assembly layer usable in flexible devices such as, for example, electronic displays, flexible photovoltaic cells or solar panels, and wearable electronics. As used herein, the term "assembly layer" refers to a layer having the following properties: (1) adhesion to at least two flexible substrates and (2) repetitive flexing to pass the durability test. Sufficient ability to remain on the adherend during the < / RTI > As used herein, a "flexible device" is a flexible device that is subjected to repeated bending or roll-up (e.g., bending) with bending radii of less than 200 mm, 100 mm, 50 mm, 20 mm, 10 mm, 5 mm, roll up operation. The acrylic-based assembly layer is flexible and is primarily elastic and has good adhesion to other flexible substrates such as plastic films or glass and has a high tolerance to shear loads. In addition, the acrylic-based assembly layer has a relatively low modulus, high percent compliance at moderate stress, low glass transition temperature, minimal peak stress during folding, and good deformation recovery after stress application and removal, Which is suitable for use in flexible assemblies. Under repeated bending or rolling of the multi-layered structure, the shear load on the adhesive layer becomes very important, and any type of stress can be caused by mechanical defects (deagglomeration, buckling of one or more layers, cavitation bubbles in the adhesive, etc.) ) As well as optical defects or Mura. Unlike traditional adhesives where the properties are predominantly viscoelastic, the acrylic-based assembly layer of the present invention is primarily elastic in service conditions, but retains sufficient adhesion to meet various durability requirements. In one embodiment, the acrylic-based assembly layer is optically transparent and exhibits low turbidity, high visible light transparency, anti-whitening behavior, and environmental durability.

The acrylic-based assembly layer of the present invention is made from selected acrylic monomer compositions and is crosslinked at different levels to provide various elastic properties, while still meeting all optical clarity requirements. For example, an acrylic-based assembly layer can be obtained that is used in a laminate with a folding radius as low as 5 mm or less, without causing delamination of the laminate or buckling or bubbling of the adhesive. In one embodiment, the acrylic-based assembly layer composition is derived from a precursor comprising at least one alkyl (meth) acrylate ester having from about 1 to about 24 carbon atoms in the alkyl group and a free-radical generating initiator.

Examples of suitable alkyl acrylates (i.e., acrylic acid alkyl ester monomers) include linear or branched monofunctional acrylates or methacrylates of non-tertiary alkyl alcohols wherein the alkyl groups have 1 to 24 carbon atoms But is not limited thereto. Examples of suitable monomers include 2-ethylhexyl (meth) acrylate, ethyl (meth) acrylate, methyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) (Meth) acrylate, isobutyl (meth) acrylate, hexyl (meth) acrylate, isooctyl (meth) acrylate, (Meth) acrylate, isodecyl (meth) acrylate, isodecyl (meth) acrylate, isobornyl (meth) acrylate, (Meth) acrylate, cyclohexyl (meth) acrylate, phenylmeth (acrylate), benzylmeth (acrylate), isostearyl acrylate and 2-methylbutyl (meth) acrylate, and combinations thereofBut is not limited thereto. Other suitable monomers include branched long chain acrylates such as those described in U.S. Patent No. 8,137,807, which is incorporated herein by reference. Additional suitable alkyl monomers include secondary alkyl acrylates such as those described in U.S. Patent Application Publication No. 2013/0260149, which is incorporated herein by reference. In one embodiment, the acrylic-based assembly layer comprises only alkyl (meth) acrylate monomers and optional vinyl esters or styrenic monomers. In such cases, the modulus and glass transition temperature (Tg) of the composition can be adjusted by selecting a combination of low and high Tg yielding monomers. In another embodiment, the acrylic-based assembly layer comprises from about 60 to about 99 parts, especially from about 65 to about 95 parts, by weight of an alkyl (meth) acrylate ester having from about 1 to about 24 carbon atoms in the alkyl group Especially about 70 to about 95 parts.

In some embodiments, the precursor composition comprises a polar copolymerizable monomer. Examples of suitable polar copolymerizable monomers include acrylic acid (AA), methacrylic acid, itaconic acid, fumaric acid, methacrylamide, N-alkylated and N, N-dialkyl substituted acrylamides or methacrylamides, Groups have up to three carbons, and N-vinyl lactams. Examples of suitable monomers include, but are not limited to, (meth) acrylamide, N-morpholino (meth) acrylate, N-vinylpyrrolidone and N-vinylcaprolactam. Other suitable polar monomers include hydroxyl-containing monomers such as 2-hydroxyethyl (meth) acrylate and 2-hydroxy-propyl (meth) acrylate, 4-hydroxybutyl (meth) Containing monomers such as 2-ethoxyethoxyethyl (meth) acrylate, 2-methoxyethoxyethyl (meth) acrylate, and the like. In one embodiment, the acrylic-based assembly layer comprises from about 1 to about 40 parts by weight, in particular from about 5 to about 35 parts, more particularly from about 5 to about 30 parts, of the polar copolymerizable monomers.

The monomer composition of the acrylic-based assembly layer may also comprise vinyl esters, and in particular C ₁ to C ₁₀ vinyl esters. Examples of suitable vinyl esters that may be purchased include, but are not limited to VeOVA 9 or VeOVA 10, vinyl acetate available from Momentive Specialty Chemicals, New Smyrna Beach, FL, USA. The vinyl ester is typically added to the monomer mixture in an amount of from about 1 part to about 20 parts by weight, especially from about 1 to about 15 parts, more particularly from about 1 to about 10 parts by weight. Other monomers, such as styrenic monomers, may also be used.

Examples of free-radical generation initiators include, but are not limited to, thermal initiators or photoinitiators. Examples of thermal initiators include, but are not limited to, peroxides such as benzoyl peroxide and its derivatives or azo compounds. Examples of commercially available azo compounds include, but are not limited to, children. VAZO 67, available from E. I. du Pont de Nemours and Co., is 2,2'-azobis- (2-methylbutyronitrile). A variety of peroxide or azo compounds are available which can be used to initiate thermal polymerization at a wide variety of temperatures. Photoinitiators may also be used in place of thermal initiators, or may be used in combination with thermal initiators. Particularly useful photoinitiators include IRGACURE 651 and Darocur 1173, both available from BASF, Tarrytown, NY, USA. The photoinitiator is typically added to the precursor mixture in an amount from about 0.01 parts to about 2 parts, especially from about 0.02 to about 1 part, more particularly from about 0.02 to about 0.5 parts, by weight.

In one embodiment, the monomer mixture comprises a multifunctional crosslinking agent. For example, the precursor mixture may include a thermal crosslinking agent that is activated during the drying step or during solvent-coated adhesive preparation, and a crosslinking agent that is copolymerized during the polymerization step. Such thermal crosslinking agents may include, but are not limited to, multifunctional isocyanates, multifunctional aziridines, and epoxy compounds. Exemplary crosslinking agents that can be copolymerized include bifunctional acrylates such as 1,6-hexane diol diacrylate or polyfunctional acrylates as known to those skilled in the art. Useful isocyanate crosslinking agents include, for example, aromatic triisocyanates available as DESMODUR N3300 from Bayer, Cologne, Germany. UV, or "UV" activated cross-linking agents may also be used to cross-link the precursor of the assembly layer. Such UV crosslinking agents may include non-co-polymerizable photo-crosslinking agents, for example, benzophenone, and acrylated or methacrylated benzophenones, such as copolymerized photo-crosslinking agents, for example, 4-acryloxybenzophenone. Typically, the crosslinking agent, if present, is added to the monomer mixture in an amount of from about 0.01 to about 5 parts by weight, especially from about 0.01 to about 4 parts, more particularly from about 0.01 to about 3 parts by weight. For example, the use of ionic cross-linking, acid-base cross-linking, or physical cross-linking methods, such as by copolymerizing high Tg markers such as polymethyl methacrylate macromer or polystyrene macromer Other cross-linking methods, such as < / RTI > The macromer can be used in an amount of from about 1 to about 20 parts by weight of the total monomer component in the assembly layer composition.

The acrylic-based assembly layer may be inherently tacky. If desired, a tackifier may be added to the precursor mixture prior to formation of the acrylic-based assembly layer. Useful tackifiers include, for example, rosin ester resins, aromatic hydrocarbon resins, aliphatic hydrocarbon resins, terpenes, and terpene phenolic resins. Generally, a light color tackifier selected from hydrogenated rosin ester, terpene, or aromatic hydrocarbon resin is preferable. When included, the tackifier is added to the precursor mixture in an amount of from about 1 part to about 50 parts, more particularly from about 5 parts to about 45 parts, most particularly from about 10 parts to about 30 parts by weight.

In one embodiment, the acrylic-based assembly layer is substantially free of acid, thereby eliminating indium tin oxide (ITO) and metal trace corrosion that could otherwise damage the touch sensor and its integrated circuit or connector. As used herein, "substantially free" means less than about 2 parts by weight, especially less than about 1 part, more particularly less than about 0.5 part by weight.

For example, other materials including molecular weight control agents, coupling agents, oils, plasticizers, antioxidants, UV stabilizers, UV absorbers, pigments, curing agents, polymer additives, nanoparticles, and other additives may be added to the monomer mixture Can be added. If the acrylic-based assembly layer needs to be optically transparent, other materials may be added to the monomer mixture, provided it does not significantly reduce the optical transparency of the assembly layer after polymerization and coating. As used herein, the term "optically transparent" means a luminous transmission of greater than about 90 percent in the wavelength range of 400 to 700 nm, a turbidity of less than about 2 percent, and an opacity of less than about 1 percent Quot;). ≪ / RTI > Both luminous transmittance and turbidity can be determined, for example, using ASTM-D 1003-92. Typically, there is no visible bubble in the optically transparent assembly layer.

The acrylic-based assembly layer monomer component may be blended with the precursor mixture. Such a precursor mixture can be pre-polymerized by exposure to heat or actinic radiation (to decompose the initiator in the mixture). This may be done prior to the addition of a cross-linking agent and other ingredients to form a coatable syrup, which may subsequently be supplemented with one or more cross-linking agents, other additives, and additional initiators. The compounded syrup is then coated on the liner or coated directly on the substrate and completely polymerized under an inert atmosphere by further exposure to UV. Alternatively, a crosslinking agent, optional additives, and an initiator may be added to the monomer, and the mixture may be both polymerized and cured in one step (e.g., as a liquid OCA). Depending on the desired coating method and viscosity, what procedure will be used will be determined.

In another process, the assembly layer monomer components may be blended with a solvent to form a mixture. The mixture may be polymerized by exposure to heat or actinic radiation (to decompose the initiator in the mixture). A crosslinking agent and additional additives, such as tackifiers and plasticizers, may be added to the solvated polymer, which may then be coated on a liner and passed through an oven to remove the solvent by drying to produce a coated adhesive film have. A solventless polymerization method such as the continuous free radical polymerization method described in U.S. Patent Nos. 4,619,979 and 4,843,134 (Kotnour et al.); An essentially adiabatic polymerization method using a batch reactor as described in U. S. Patent No. 5,637, 646 (Ellis); And U.S. Patent No. 5,804,610 (Hamer et al.), Can also be used to prepare the polymer.

The disclosed compositions or precursor blends can be coated by any of a variety of techniques known to those skilled in the art, such as roll coating, spray coating, knife coating, die coating, and the like. Alternatively, the precursor composition may also be delivered as a liquid to fill the gaps between the two substrates, followed by exposure to heat or UV to polymerize and cure the composition between the two substrates.

The present invention also provides a laminate comprising an acrylic-based assembly layer. A laminate is defined as a multi-layer composite in which at least one assembly layer is interposed between two flexible substrate layers or layers thereof. For example, the composite may comprise a three-layer composite of a substrate / assembly layer / substrate; Substrate / assembly layer / substrate / assembly layer / substrate 5 layer composite. Though the thickness, mechanical properties, electrical properties (e.g., dielectric constant), and optical properties of each flexible assembly layer in such a multilayer stack may be the same, they may improve the design and performance characteristics of the final flexible device assembly better It can also be different to match. The laminate has at least one of the following properties: optical transparency over the useful life of the article in which the laminate is used, ability to maintain sufficient bond strength between the layers of the article in which the laminate is used, resistance to, or avoidance of, , And resistance to bubbling over its useful life. The resistance to bubble formation and the maintenance of optical transparency can be evaluated using an accelerated aging test. In the accelerated aging test, an acrylic-based assembly layer is placed between two substrates. The resulting laminate is then exposed to high temperatures often combined with high humidity for a period of time. Even after exposure to high temperatures and humidity, laminates comprising an acrylic-based assembly layer will maintain optical transparency. For example, the acrylic-based assembly layer and the laminate remain optically clear after aging for approximately 72 hours at 70 < 0 > C and 90% relative humidity and subsequently cooling to room temperature. After aging, the average transmittance of the adhesive at 400 nanometers (nm) to 700 nm is greater than about 90% and the turbidity is less than about 5%, especially less than about 2%.

In use, the acrylic-based assembly layer may have a number of fold cycles (e.g., from about -30 DEG C, -20 DEG C, or -10 DEG C) to a much lower temperature than the freezing point over a wide temperature range of about 70, 85, Will resist fatigue for a while. In addition, since the display comprising the acrylic-based assembly layer can be statically placed in a folded state for several hours, the acrylic-based assembly layer has minimal or no creep to prevent significant deformation of the display, Even if it can be recovered, it can only be recovered only partially. This permanent deformation of the acrylic-based assembly layer or of the panel itself may lead to optical distortions or unacceptable in the display industry. Thus, the acrylic-based assembly layer not only tolerates high temperature and high humidity (HTHH) test conditions, but also withstand the considerable flexural stress caused by folding the display device. Most importantly, the acrylic-based assembly layer has an exceptionally low storage modulus and high elongation over a wide temperature range (including temperatures much lower than the freezing point; therefore, a low glass transition temperature is preferred) and is crosslinked To produce an elastomer that has little or no creep under static loads.

During the folding or unfolding event, the acrylic-based assembly layer is expected to undergo significant deformation and cause stress. This stress-resistant force will be determined in part by the modulus and thickness of the layer of the foldable display comprising the acrylic-based assembly layer. In order to ensure good resistance to folding as well as good performance, minimum stress generation, and good dissipation of stresses associated with bending events, the acrylic-based assembly layer is often formed of a sufficient Have low storage or elastic modulus. To further ensure that such behavior is consistently maintained over the expected operating temperature range of such a device, the G 'change over a wide range of relevant temperatures is minimal. In one embodiment, the relevant temperature range is from about -30 캜 to about 90 캜. In one embodiment, the shear modulus is less than about 2 MPa, especially less than about 1 MPa, more particularly less than about 0.5 MPa, most particularly less than about 0.3 MPa over the entire relevant temperature range. It is therefore desirable to place the glass transition temperature (Tg), that is, the temperature at which the material transitions to the vitreous state, with a corresponding change in G 'to a value typically above about 10 ⁷ Pa, desirable. In one embodiment, the Tg of the acrylic-based assembly layer in the flexible display is less than about 10 占 폚, especially less than about -10 占 폚, more particularly less than about -30 占 폚. As used herein, the term "glass transition temperature" or "Tg" means that the polymeric material is in a gummy state (e.g., Flexible < / RTI > and elastomeric). The Tg can be determined using techniques such as dynamic mechanical analysis (DMA), for example. In one embodiment, the Tg of the acrylic-based assembly layer in the flexible display is less than about 10 占 폚, especially less than about -10 占 폚, more particularly less than about -30 占 폚.

The assembly layer is typically coated with a dry thickness of less than about 300 micrometers, especially less than about 50 micrometers, especially less than about 20 micrometers, more particularly less than about 10 micrometers, and most particularly less than about 5 micrometers. The thickness of the assembly layer can be optimized according to its position in the flexible display device. It may be desirable to reduce the thickness of the assembly layer to reduce the overall thickness of the device as well as minimize buckling, creep, or delamination failure of the composite structure.

The ability of the acrylic-based assembly layer to absorb bending stresses and conform to the rapidly changing geometry of the bends or folds can be characterized by the ability of such materials to undergo a large amount of strain or elongation under the associated applied stress . This conformance behavior can be investigated through a number of methods including conventional tensile elongation tests as well as shear creep tests. In one embodiment, in the shear creep test, the acrylic-based assembly layer has a thickness of from about 6 to about 500 mils, particularly from about 20 mils to about 300 mils, more particularly from about 50 mils to about 200 mils, × 10 ^-6 1 / Pa or more, particularly about 20 × 10 ^-6 1 / Pa, greater than or equal to about 50 × 10 ^-6 1 / Pa or more, more particularly at least about 90 × 10 ^-6 1 / Pa shear creep compliance (J) . This test is usually performed at room temperature, but may also be performed at any temperature associated with the use of the flexible device.

The acrylic-based assembly layer also exhibits relatively low creep to avoid continuous deformation in the multilayer composite of the display after repeated folding or bending events. The material creep can be measured through a simple creep experiment in which a constant shear stress is applied to the material over a given amount of time. Once the stress is removed, the recovery of the induced strain is observed. In one embodiment, the shear strain recovery rate within 1 minute after removing the applied stress at room temperature (at at least one point of applied shear stress in the range of from about 5 kPa to about 500 kPa) At least about 50%, in particular at least about 60%, at least about 70%, and at least about 80%, more particularly at least about 90% This test is usually performed at room temperature, but may also be performed at any temperature associated with the use of the flexible device.

In addition, the ability of the acrylic-based assembly layer to generate minimum stresses and dissipate stress during folding or bending events is advantageous because the acrylic-based assembly layer protects the more fragile components of the flexible display assembly as well as the ability to avoid inter- It is important for his ability to do. Stress generation and dissipation can be measured using a traditional stress relaxation test in which the material is forced to the relevant shear deformation and then held at that deformation. The amount of shear stress is then monitored over time as the material is held in this target deformation. In one embodiment, the residual stresses observed after 5 minutes (measured shear stresses to peak shear stresses, measured after 5 minutes, after about 500% shear strain, especially about 600%, about 700%, and about 800% Is less than about 50%, especially less than about 40%, less than about 30%, and less than about 20%, more particularly less than about 10% of the peak stress. This test is usually performed at room temperature, but may also be performed at any temperature associated with the use of the flexible device.

As an assembly layer, the acrylic-based assembly layer must adhere well to adjacent layers in the display assembly to prevent delamination of the layer during use of the device, including repeated bending and folding operations. The exact layer of the composite will be specific to the device, but the adhesion to a standard substrate such as PET can be used to measure the general adhesion performance of the assembly layer in the conventional 180 degree peel test mode. The adhesive may also require a sufficiently high cohesive strength to be measured, for example, as a laminate of the assembly layer material between two PET substrates in a conventional T-peel mode.

When laying an acrylic-based assembly layer between two substrates to form a laminate and folding or bending the laminate and keeping it at the relevant radius of curvature, the laminate is subjected to buckling or de-lamination at all operating temperatures (-30 캜 to 90 캜) This is an event to indicate material failure in the flexible display device. In one embodiment, the multilayer laminate containing the acrylic-based assembly layer has a thickness of less than about 200 mm, less than about 100 mm, less than about 50 mm, particularly less than about 20 mm, less than about 10 mm, and Do not exhibit fracture when placed in a channel that forces a radius of curvature of less than about 5 mm, more particularly less than about 2 mm. Also, when the laminate comprising the acrylic-based assembly layer of the present invention does not exhibit continued deformation and returns to a rather flat or nearly flat orientation, when it is removed from the channel and allowed to return to its previous flat orientation from the bent orientation. In one embodiment, the laminate was held for 24 hours and then removed from the channel holding the laminate with a radius of curvature of less than about 50 mm, especially less than about 20 mm, less than about 10 mm, and less than about 5 mm, The composite has a final angle between the laminate, laminate bending point, and return surface of less than about 50 degrees, more specifically less than about 40 degrees, less than about 30 degrees, and less than about 20 degrees, more particularly less than about 50 degrees, And returns to a nearly flat orientation of less than about 10 degrees. In other words, the angle of inclination between the flat portions of the folded laminate is greater than about 130 degrees, especially greater than about 140 degrees, greater than about 150 degrees, and greater than about 160 degrees, within about 1 hour after the laminate is taken out of the channel, More particularly more than about 170 degrees. This return is preferably obtained under normal use conditions, including after exposure to the durability test conditions.

In addition to the static folding test behavior described above, a laminate comprising a first substrate and a second substrate bonded to an acrylic-based assembly layer does not exhibit destruction such as buckling or de-lamination during the dynamic folding simulation test. In one embodiment, the laminate has a flexural modulus of greater than about 10,000 fold cycles, particularly about 20,000 fold cycles with a radius of curvature of less than about 50 mm, especially less than about 20 mm, less than about 10 mm, and less than about 5 mm, All use for dynamic folding tests in free bending mode (ie, no mandrel is used) of more than about 40,000 fold cycles, more than about 60,000 fold cycles, and more than about 80,000 fold cycles, more particularly more than about 100,000 fold cycles And does not exhibit destruction events between temperatures (-30 ° C to 90 ° C).

To form the flexible laminate, the assembly layer of the present invention is positioned between the first and second substrates to bond the first substrate to the second substrate. Additional layers may also be included to make the multilayer stack. Subsequently, pressure and / or heat is applied to form a flexible laminate.

Example

Since many modifications and variations within the scope of the present invention will be apparent to those skilled in the art, the present invention is described in further detail in the following embodiments, which are intended as illustrations only. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by weight.

[Table 1]

Test Method 1. Optical Characteristics

Turbidity measurements were made in a transmission mode using an UltrascanPro spectrophotometer from HunterLab (Reston, VA, USA). The assembly layer was coated between release-coated carrier liners (RF02N and RF52N, SKC Haas, Korea), cut to a length of approximately 5 cm wide x 10 cm, and the thickness measured. One of the carrier liner was removed and the sample was laminated to a 1 mm thick clear glass. The other liner was then removed and a 2 mil thick layer of optically transparent polyethylene terephthalate (PET, SKYROL SH-81 from SK Chemicals Co., Ltd., South Korea) was laminated onto the assembly layer. Samples were placed in an Ultrascan Pro spectrophotometer to measure transmittance and color through PET / OCA / glass assemblies. Additional samples were prepared and aged for 800 hours in a chamber set at 65 占 폚 and 90% relative humidity. After the sample was taken out of the humidity chamber and allowed to cool, the turbidity measurement was again performed. Typically, acceptable samples for optical applications will have a turbidity value of less than about 5%, especially less than about 2%, and a b * color value of less than about 5.

Test method 2. Dynamic mechanical analysis

Dynamic mechanical analysis was used to determine the glass transition temperature (T _g ) of the material as well as to examine the modulus as a function of temperature. An 8 mm diameter x approximately 1 mm thick disc of assembly layer was placed between the probes of a DHR parallel plate rheometer (TA Instruments, Newcastle, Del.). Temperature scans were performed by ramping from -45 ° C to 50 ° C at 3 ° C / min. During this ramping, the sample was oscillated at a frequency of 1 Hz and a strain of approximately 0.4%. Shear storage modulus (G ') was recorded at the selected main temperature. The T _g of the material as a peak in the tan delta versus temperature profile was also determined. In order to ensure sufficient compliance of the assembly material over a typical operating temperature range, the shear storage modulus is preferably less than about 2 MPa over the entire temperature range of from about -20 캜 to about 40 캜, as measured using the tests described above Do.

Test method 3. Creep test

An assembly layer sample was creep tested by placing a 8 mm diameter x 0.25 mm thick disc in a DHR parallel plate rheometer and applying a shear stress of 95 동안 for 5 seconds to remove the applied stress, To be restored. The peak shear strain at 5 seconds and the amount of strain recovery after 60 seconds were recorded. The shear creep compliance (J) at any point in time after the application of the stress is defined as the ratio of the shear strain at that point divided by the applied stress. In order to ensure sufficient compliance within the assembly layer, it is preferred that the peak shear strain after application of the load in the tests described above is greater than about 200%. Moreover, in order to minimize material creep in the flexible assembly, it is desirable that the material is recovered in excess of about 50% strain at 60 seconds after applied stress relief. The percent recoverable strain is defined as ((S ₁ -S ₂ ) / S ₁ ) * 100, where S ₁ is the shear strain recorded at the peak at 5 seconds after stress application and S ₂ is the shear strain recorded at peak Is the shear deformation measured at.

Test method 4. Stress relaxation test

A 8 mm diameter x 0.25 mm thick disc was placed in a DHR parallel plate rheometer and a 900% shear strain was applied to perform a stress relaxation test on a sample of the assembly layer. The peak attenuation resulting from this deformation as well as the stress attenuation over a period of 5 minutes were recorded. The stress relaxation was calculated by the following formula: (1- (S _f -S _p )) * 100%. Where S _p and S _f are the shear stresses recorded at the peak and final (5 minutes) point.

Test method 5. T-peel test

An assembly layer approximately 0.05 mm thick was laminated between two primed polyester layers with a thickness of 0.075 mm. From this laminate, strips 1 inch wide by 6 inch long were cut for testing. The ends of each strip were placed in the tensile grips of an Instron (Instron, Norwood, Mass., USA). Then, the peel adhesion (in grams) was measured while the structure was peeled at a rate of 50 mm / min. Three peeling tests were performed for each example and the peeling forces obtained were averaged.

Test method 6. Static folding test

A two-mil thick section of the assembly layer was laminated between 1.7 mil polyimide (PI) sheets to produce a three-layer structure, which was then cut to a length of 5 inches. In addition, a five-layer structure consisting of PI / AS / PI / AS / PI was also prepared in a similar manner using a two-mil assembly layer and 1.7 mil PI. A laminate structure was also prepared in a similar manner using a 4 and 6 mil thick assembly layer between the layers of the PI. The sample was then bent around a 3 mm radius of curvature and held there for 24 hours. After 24 hours, the sample was observed and passed a static retention test if no buckling or delamination of the adhesive was indicated at all. In addition, the sample was released and restored after 24 hours, and the time required to achieve 90 degrees and 45 degrees angles (i.e., 90 degrees and 135 degrees inclusions, respectively) for the plane as well as the final angle ) Were recorded. In some cases, the sample could not recover 45 degrees or even 90 degrees to the plane within 3 minutes of testing time. For these samples, the final angle was recorded at the lowest value achieved during that period. The static folding test was also repeated, holding the sample at a temperature of -20 DEG C for a period of 24 hours.

Test method 7. Dynamic folding test

The liner was removed from the 2 mil thick assembly layer and the material was laminated between two 1.7 mil polyimide sheets to produce a three layer structure. The laminate was then cut into 5 "length x 1" widths. A five-layer structure consisting of PI / AS / PI / AS / PI was also prepared in a similar manner using a two-mill assembly layer and 1.7-mil PI. The sample was mounted on a dynamic folding device with two folding tables rotating at 0 degrees (i.e., the sample now folded) at 180 degrees (i.e., the sample was not bent), and the sample was tested at a test speed of 100,000 Cycle. The bending radius of 5 mm was determined by the clearance between the two rigid plates in the closed state (0 degree). The mandrel was not used to guide the curvature (i.e., the free bending method was used). Folding was performed at room temperature.

Test method 8. Determination of molecular weight distribution

The molecular weight distribution of the resulting polymer was characterized using conventional gel permeation chromatography (GPC). GPC instruments available from Waters Corporation (Milford, Mass.) Were equipped with a high pressure liquid chromatographic pump (Model 1515 HPLC), an autosampler (Model 717), a UV detector (Model 2487), and a refractive index detector (Model 2410) . The chromatograph was equipped with two 5 micrometer PLgel MIXED-D columns available from Varian Inc .; Palo Alto, Calif., USA.

The polymer or dried polymer material was dissolved in tetrahydrofuran at a concentration of 0.5% (weight / volume) and passed through a 0.2 micrometer polytetrafluoroethylene filter available from VW Aluminum (West Chester, PA, USA) And filtered to prepare a sample of the polymer solution. The resulting sample was injected into GPC and eluted at a rate of 1 milliliter per minute through a column maintained at 35 < 0 > C. Calibration curves were established by calibrating the system with polystyrene standards using linear least squares fit analysis. The weight average molecular weight (M _w ) and the polydispersity index (weight average molecular weight divided by number average molecular weight) of each sample were calculated against this standard calibration curve.

Examples 1 to 6: Preparation of solvent-based assembly layer samples.

An assembly layer film was prepared according to the composition provided in Table 2 below. In Example 1, 40 g of 2EHA, 10 g of HBA, 0.05 g of Vaso 67, 0.025 g of TDDM, and 50 g of ethyl acetate were added to the vial. The contents were mixed and purged with nitrogen for 2 minutes then sealed and placed in a Laundrometer (SDL Atlas, Rock Hill, South Carolina, USA) spinning bath at 60 ° C for 24 hours. After 24 hours, the sample was analyzed using GPC and it was determined that the polymer had an M _w of 465 kDa and a polydispersity index of 5.75. Then, 0.037 g of N3300 crosslinking agent was added to this solution and mixed for 2 hours, then, using a knife coater with a 5-mil gap, a 50 micrometer thick RF02N silicone treated polyester release liner Haas). After the coated samples were placed in an oven at 70 DEG C for 24 hours, the upper carrier layer of a T50 silicone treated polyester release liner (Solutia, USA) was laminated to the assembly layer. This procedure was repeated for Examples 2 to 6 and Comparative Example CE1 and Comparative Example CE2 using the formulations provided in Table 2.

[Table 2]

Examples 7 to 20: Preparation of a solvent-free assembly layer sample.

An assembly layer film was also prepared according to the formulation provided in Table 3 using the following procedure, which was provided in detail for Example 7. In a clear glass bottle, 80 g of 2-EHA, 20 g of HBA and 0.02 g of D1173 photoinitiator were mixed. Samples were purged with nitrogen for 5 minutes and exposed to low intensity (0.3 mW / cm2) UV from a 360 nm LED light source until a coatable viscosity (about 2000 cP) was achieved. The LED light source was turned off and purged with air to stop the polymerization. An additional 0.18 g of D1173 photoinitiator and 0.01 g of HDDA crosslinker were then added to the formulation as indicated in Table 3 and mixed overnight. The viscous polymer solution was then coated between silicone treated polyester release liner, RF02N and T50, using a knife coater with a set clearance to obtain an OCA coating thickness of 2 mil unless otherwise specified. This structure was then irradiated with UV-A at a total dose of 1500 mJ / cm 2 with a black light lamp. The comparative example is listed as CE3.

[Table 3]

Examples 1 to 19 and Comparative Example CE1, Comparative Example CE2 and Comparative Example CE3 were tested for T _g , modulus, shear creep, and stress relaxation properties as described in Test Method 2 to Test Method 4 described above Respectively. Data are recorded in Table 4 below.

[Table 4]

Examples 8 to 20 and Comparative Example CE3 were tested for optical properties, tensile elongation and T-peel adhesion according to Test Method 1, Test Method 5 and Test Method 6, and the results are shown in Table 5 have. The T-peel failure mode is reported as adhesion (Ad), cohesion (Co), or transfer (Tr, some cohesive failure / ghosting).

[Table 5]

All samples were tested under static bending conditions as indicated by Test Method 6 and the selected samples were tested for dynamic bending performance as described in Test Method 7. [ The results are provided in Table 6 below.

[Table 6]

[Table 7]

Although the present invention has been described with reference to preferred embodiments, those skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.

Claims (21)

An assembly layer for a flexible device,
The assembly layer
Alkyl (meth) acrylate esters having from 1 to 24 carbon atoms in the alkyl group; And
Is derived from a precursor comprising a free radical generation initiator,
Within a temperature range of from about -30 DEG C to about 90 DEG C, the assembly layer has a shear storage modulus of about 2 MPa or less at a frequency of 1 Hz, an applied shear stress of about 50 kPa to about 500 kPa Of shear creep compliance (J) measured at 5 seconds is greater than or equal to about ⁶ x 10 < ^-6 > 1 / Pa, and within about 1 minute after removal of applied shear stress, An assembly layer having a strain recovery of at least about 50% at at least one point of shear stress. 2. The optically transparent assembly layer of claim < RTI ID = 0.0 > 1, < / RTI & The assembly of claim 1, wherein the flexible device is a flexible electronic display. The assembly of claim 1, comprising from about 60 to about 95 weight percent of an alkyl (meth) acrylate ester having from 1 to 24 carbon atoms in the alkyl group. The assembly of claim 1, wherein the assembly layer has a glass transition temperature of about 10 캜 or less. The assembly of claim 1, further comprising a polar copolymerizable monomer. The assembly of claim 1, further comprising at least one of a tackifier, a molecular weight controller, a plasticizer, a stabilizer, a crosslinking agent, and a coupling agent. A first flexible substrate;
A second flexible substrate; And
An assembly layer positioned between the first flexible substrate and the second flexible substrate and in contact with the first flexible substrate and the second flexible substrate,
The assembly layer
Alkyl (meth) acrylate esters having from 1 to 24 carbon atoms in the alkyl group; And
Is derived from a precursor comprising a free radical generation initiator,
Within a temperature range of from about -30 ° C to about 90 ° C, the assembly layer has a shear storage modulus at a frequency of 1 Hz of about 2 MPa or less, measured at 5 seconds with an applied shear stress of about 50 kPa to about 500 kPa (J) of at least about ⁶ x 10 < ^-6 > 1 / Pa and less than about 1 x 10 < ^-6 > A laminate having a strain recovery of at least about 50%. 9. The laminate of claim 8, wherein the assembly layer is an optically clear laminate. 9. The laminate of claim 8, wherein at least one of the first substrate and the second substrate is an optically clear laminate. 9. The laminate of claim 8, wherein the assembly layer comprises from about 60 to about 95 weight percent of an alkyl (meth) acrylate ester having from 1 to 24 carbon atoms in the alkyl group. 9. The laminate of claim 8, wherein the assembly layer further comprises a polar copolymerizable monomer. 9. The laminate of claim 8, wherein the assembly layer has a glass transition temperature of about 10 DEG C or less. 9. The laminate of claim 8, which does not exhibit fracture when placed in a channel that forces a radius of curvature of less than about 15 mm over a period of 24 hours at room temperature. 15. The laminate of claim 14, wherein after removing from the channel after 24 hours at room temperature, the laminate returns to a subtended angle of about 130 degrees or more. 9. The laminate of claim 8, which does not exhibit fracture when subjected to a dynamic folding test at room temperature at a flexural cycle of about 10,000 with a radius of curvature of less than about 15 mm. A method for bonding a first substrate and a second substrate,
Both of the first and second substrates are flexible,
The method
Placing the assembly layer between the first and second flexible substrates to form a laminate; And
Applying at least one of pressure and heat to form a laminate,
The assembly layer
Alkyl (meth) acrylate esters having from 1 to 24 carbon atoms in the alkyl group; And
Is derived from a precursor comprising a free radical generation initiator,
Within a temperature range of from about -30 ° C to about 90 ° C, the assembly layer has a shear storage modulus at a frequency of 1 Hz of about 2 MPa or less, measured at 5 seconds with an applied shear stress of about 50 kPa to about 500 kPa (J) of at least about ⁶ x 10 < ^-6 > 1 / Pa and less than about 1 x 10 < ^-6 > Wherein the strain recovery rate is at least about 50%. 18. The method of claim 17, wherein the assembly layer is optically transparent. 18. The method of claim 17, wherein the laminate does not exhibit fracture when placed in a channel that forces a radius of curvature of less than about 15 mm over a period of 24 hours at room temperature. 20. The method of claim 19, wherein the laminate is withdrawn from the channel after a period of 24 hours at room temperature and then returned to a subtended angle of greater than about 130 degrees. 18. The method of claim 17, wherein the laminate does not exhibit fracture upon dynamic flexure testing at room temperature above about 10,000 fold cycles at a radius of curvature of less than about 15 mm.